1. Field of the Invention
The present invention relates to a multilayer capacitor that not only can realize both downsizing and higher capacity, but also has reliability not lowered with time, and more particularly, to that suitable for use as a multilayer ceramic chip capacitor.
2. Description of the Related Art
A multilayer capacitor such as a multilayer ceramic chip capacitor having a sandwich structure in which dielectric layers made of ceramic and internal electrodes are stacked has been conventionally known. As a device on which such a multilayer capacitor is to be mounted is becoming more downsized and coming to have a higher performance, further downsizing of the multilayer capacitor and further increase in its capacitance are rapidly underway in recent years. In order to realize both downsizing and higher capacity of the multilayer capacitor, it is basically necessary to reduce the thickness per layer of the dielectric layers to make a further multilayered structure.
Further, in the multilayer capacitor, there exist dummy portions formed only of dielectrics and serving as margins on upper, lower, right, and left sides of a portion formed of a stack of dielectric layers and internal electrodes. In recent years, these upper, lower, right, and left dummy portions without any internal electrode tend to be reduced in size in accordance with the aforesaid downsizing and increase in capacity.
Conventionally, on the other hand, the size of the dummy portions has not been specifically stipulated, and the dimension to a degree not causing a lowered yield in a manufacturing process of the multilayer capacitors was secured. However, in order to exclude defective products, not only the total inspection of the multilayer capacitors before shipment is conducted for checking their electric properties, but also a high voltage is applied for screening in order to exclude products having a low level of withstand voltage and thus not satisfying a predetermined specification.
However, since ceramic which is a ferroelectric substance exhibits a property as a piezoelectric element, it expands when a high voltage is applied thereto. Therefore, when a high voltage is applied to the multilayer capacitor, a thickness dimension T of a portion of a dielectric layer 116 sandwiched between internal electrodes 114 greatly expands from the state shown in FIG. 6(A) to be brought into the state shown in FIG. 6(B), while the expansion of dummy portions to which practically no high voltage is applied is small.
Consequently, a difference in expansion between these portions sometimes causes a crack C in a multilayer body 112 shown in FIG. 7 since ceramic has no malleability. When the crack C exists in the multilayer body 112, reliability of the multilayer capacitor may possibly be lowered with time.